Rev. Col. Bras. Cir. 2016; 43(3):

INTRODUCTION

The endovascular treatment of abdominal aortic an-

eurysms has become an increasingly used surgical

alternative instead of traditional surgery1. Treatment is

successful when there is full suppression of blood flow

and systemic pressure in the aneurysmal sac, which pre-

vent rupture2-4. Although we have achieved significant

technological advances since the first generation of aortic

stents, recent information from late postoperative fol-

low-up have shown a significant percentage of compli-

cations requiring surgical reintervention. The reason for

treatment failure, in many cases, is still connected to the

endoprosthesis used (type III leakage) 5-7.

Studies have focused on the deterioration of

the currently marketed prosthetic material, which is made

by the association of a metal structure with PTFE or poly-

ester coating8-10. Thus arises a new therapeutic method,

based on experimental haemodynamic studies, the mul-

tilayered stents: uncoated metal prostheses, capable of

promoting redirection of blood flow within the aneurysm

sac, preventing its expansion and rupture, even without

total flow abolition in the aneurysmal sac8-14.

The aim of this study is to experimentally an-

alyze the effects of the implant, in pigs, of three stents

with the same design (triple stent) on the redirection of

blood flow of the aneurysmal sac, and to determine pos-

sible changes in the abdominal aorta blood flow pattern

after treatment.

METHODS

The research project was approved by the Eth-

ics in Research Committee of the Universidade Estadual

de Ciências da Saúde de Alagoas (UNCISAL) Protocol 61-

A, and strictly followed the ethical principles of animal

experimentation of the Colégio Brasileiro de Experimen-

tação Animal (COBEA), based on Resolution 714/02 of

the Conselho Federal de Medicina Veterinária15,16.

The sample consisted of seven female pigs

from the crossing of Landrace and Large White, weigh-

ing 20 to 25 kg, supplied by the same producer, proper-

DOI: 10.1590/0100-69912016003004

Alterations of blood flow pattern after triple stent endovascular treatment of saccular abdominal aortic aneurysm: a porcine model.

Alterações do padrão do fluxo sanguíneo após tratamento endovascular do aneurisma sacular da aorta abdominal com triplo stent: modelo em suínos.

Jahir richard de Oliveira1; MauríciO de aMOriM aquinO1; Svetlana BarrOS2; GuilherMe BenJaMin BrandãO Pitta3; adaMaStOr huM-

BertO Pereira3.

1 - Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brasil; 2 - Universidade Estadual de Ciências da Saúde de Alagoas (UNCI-SAL), Maceió, AL, Brasil; 3 - Programa de Pós-Graduação em Ciências Cirúrgicas do Departamento de Cirurgia da Faculdade de Medicina da Univer-sidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brasil.

Original Article

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A B S T R A C T

Objective: to determine the blood flow pattern changes after endovascular treatment of saccular abdominal aortic aneurysm with triple stent.

Methods: we conducted a hemodynamic study of seven Landrace and Large White pigs with saccular aneurysms of the infrarenal abdominal

aorta artificially produced according to the technique described. The animals were subjected to triple stenting for endovascular aneurysm. We

evaluated the pattern of blood flow by duplex scan before and after stent implantation. We used the non-paired Mann-Whitney test for sta-

tistical analysis. Results: there was a significant decrease in the average systolic velocity, from 127.4cm/s in the pre-stent period to 69.81cm/s

in the post-stent phase. There was also change in the flow pattern from turbulent in the aneurysmal sac to laminate intra-stent. Conclusion:

there were changes in the blood flow pattern of saccular abdominal aortic aneurysm after endovascular treatment with triple stent.

Keywords: Regional Blood Flow. Sacular Aneurysm. Aortic Aneurysm, Abdominal. Stents. Swine.

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Rev. Col. Bras. Cir. 2016; 43(3):

ly vaccinated and dewormed according to the age. We

submitted them to the artificial production of infrarenal

abdominal aortic aneurysms according to the modified

technique of Perini17 as described: transabdominal expo-

sure of the abdominal aorta, with xyphopubic median

incision, followed by aortic exposure through circumfer-

ential dissection between the renal arteries and the distal

trifurcation (common iliac arteries and internal iliac artery

trunk); election of a 3cm segment for making of the an-

eurysm, the branches repaired with 3.0 linen thread, and

administered intravenous heparin (100IU/kg); clamping

of the aorta proximal and distal to the chosen segment

and conduction of a longitudinal arteriotomy followed by

the patch suture with bovine pericardium in the form of

a previously prepared bag of 3x3 cm, 6.0 polypropylene

continuous sutures (Figure 1); Fifteen days after surgery,

we performed Duplex Scan evaluation to confirm the

aneurysms patency, as well as analyze the pre-stenting

blood flow parameters. Then they underwent triple stent

implantation and reevaluation of blood flow to assess the

variables. Anesthesia was performed following the CCEB/

UNCISAL general anesthesia protocol for porcine.

Stents Implantation

Vascular access to aortography was obtained

by surgical dissection of the right femoral artery, and the

arterial puncture performed under direct vision with a 16

Jelco catheter. After the advance of a 0.035x260 cm an-

gled tip hydrophilic guidewire, we introduced a 11 cm 5F

sheath. We advanced the sheath under fluoroscopic con-

trol until the common iliac artery. Further, we performed

the aortography with a 100 cm 5F MP angiographic cath-

eter to identify the aneurysm, follow by the positioning

of the catheter in the thoracic aorta, above the aneurysm

site.

We later performed the vascular access for the

implantation of stents through surgical dissection of the

right carotid artery, the arterial puncture being performed

under direct vision with a 16 Jelco. After the advance of

0.035x260 cm angled tip hydrophilic guidewire, we intro-

duced a 11 cm 7F sheath. We advanced the sheath under

fluoroscopic control until the aortic arch, and positioned

the guidewire in the thoracic aorta with the aid of an IM

catheter.

After positioning of the femoral catheter within

the aneurysmal sac to angiographic control, we proceded

to the sequential insertion with deployment of the stents

through the right carotid artery, in the following order of

sizes: 8x40 mm, 9x40 mm and 10x40 mm, starting the

deployment from the porcine aorta trifurcation. Then, we

carreid out a control aortography with a 5F MP angio-

graphic catheter via the right carotid artery (Figure 2).

The nitinol stents used in the experiment were

manufactured by the company Braile Biomedica (Brazil),

of self-expanding type, with an over-the-wire deploy-

ment system, compatible with a 7F introducer. The stent

features a closed cell design, with monofilament braids in

tubular form, in diamond shape, with proximal and distal

radiopaque markers in gold.

We recorded the images through the Duplex

OliveiraAlterations of blood flow pattern after triple stent endovascular treatment of saccular abdominal aortic aneurysm: a porcine model

154-159

Figure 1. Saccular aneurysm after blood flow release. Figure 2. Aortography post-stent implantation.

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Rev. Col. Bras. Cir. 2016; 43(3):

Scan 30 minutes before the stents implantation and 30

minutes after the procedure.

We evaluated the images as for the flow pat-

tern change, turbulent and laminar, as well as for the

peak systolic velocity obtained in the aneurysmal aorta.

We also evidenced the change of flow pattern from tur-

bulent to laminar after the stent release by aortography.

Study variables

Primary Variable

Change in the blood flow pattern after endovas-

cular treatment of saccular aortic aneurysm. We quantified

the flow by vascular ultrasound, using a portable device.

Secondary Variables

Average blood flow velocity in the aorta; fre-

quency of thrombosis in the aneurysmal sac.

As additional information, we evaluated the av-

erages of the animals ages, of their weights and of the

procedure time.

We performed the statistical analysis using the

unpaired Mann-Whitney test and calculating the confidence

interval (CI) of 95% for each point estimate. We evaluated

the statistical hypotheses H0 (pre-stent flow equals post-

stent flow) and H1 (pre-stent flow is not equal post-stent

flow) with the GraphPad Instat Prism 5 (2012) statistical pro-

gram for Windows. The sample size was based on previous

studies on the subject conducted in pigs18-21.

RESULTS

All seven animals were successfully submitted

to implantation of stents without technical difficulty. The

surgical procedure time was 190 minutes, and we did not

observe any complications such as malposition, migration

or inadequate expansion of stents.

In table 1, we describe the quantitative vari-

ables that constitute Systolic Peak velocity (PSV) and resis-

tance index (RI) before and after the triple stenting, which

revealed significant changes, i.e., loss of systolic velocity

after placement of stents, as well as the fall in resistance

index in many animals. Regarding systolic velocity, we ob-

served a significant decrease with an average pre-stent

velocity 127.4cm/s (95% CI 79.93±0174.8) and a mean

post-stent velocity 69,81 cm/s (95% CI 40.18±99.43),

confirming the change in blood flow patterns.

The qualitative variables, which represent the

change in the flow pattern from turbulent in the aneurys-

mal sac to laminar intrastent after treatment with triple

stent, were demonstrated through the duplex scan (Fig-

ures 3 and 4).

DISCUSSION

The treatment of abdominal aortic aneurysms by

endovascular technique has been performed with increasing

frequency. This has lead to the increased observation of leaks

related to the endoprosthesis6, usually due to early defects of

components or material fatigue. Recently, a new kind of stent

OliveiraAlterations of blood flow pattern after triple stent endovascular treatment of saccular abdominal aortic aneurysm: a porcine model

Figure 3. Pre-stent aneurysm in animal 1. Figure 4. Post-stent aneurysm.

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Rev. Col. Bras. Cir. 2016; 43(3):

came up that brought a different concept for the treatment

of aneurysms12. These stents with multiple layers allow the

redirection of the flow in the aneurysmal sac, leading to loss

of local pressure and preventing expansion.

Several models of assessment of aortic aneu-

rysm flow have been described. Through the dynamics

analysis of aortic flow one observes the flow behavior and

compares stents and endoprosthesis in the treatment of

aortic aneurysms. It is therefore apparent that the pres-

sure and flow pattern changes occur due to change in

the systolic velocity during stent use. Augsburger et al.,

through a silicone aneurysm model, also present findings

of changes in the flow pattern, as well as the change in

the volume flow after aneurysm stenting13. Jiang et al.,

on their turn, evaluated the default behavior of the flow

through angiography and computer simulations of fluid

dynamics in dogs with artificially produced aneurysms22.

In this pioneering study, we used an experi-

mental model in pigs to assess the changes in the flow

pattern with duplex scan after triple stent implantation

for the treatment of aortic aneurysm in animals previously

submitted to the making of aneurysmal sac with bovine

pericardium by the modified Perini technique17.

Changes in blood flow pattern in this study were

evaluated through duplex scan analysis. Two analyzes were

carried out, one in the animal with the aneurysm before

the stents implantation, the and other after implantation

of stents. We obtained the blood flow pattern analysis and

also the parameters systolic velocity and resistance index.

The systolic velocity showed a significant de-

crease, with an average pre-stent velocity of 127.4cm/s

(95% CI 79.93±174.8) and a mean post-stent veloci-

ty of 69.81cm/s (95% CI 40.18±99.43), confirming the

change in blood flow patterns.

Images by duplex scan showed change in the

flow pattern, ie, from turbulent in the aneurysmal sac to

laminar intrastent, the aneurysmal sac presenting with

blood flow or excluded. Doppler ultrasonography in pigs

showed the possibility to analyze not only the presence

of flow within the aneurysmal sac, but also the hemody-

namic features of such flow, with more information.

In conclusion, this study showed changes in the

blood flow pattern of saccular abdominal aortic aneu-

rysms after endovascular treatment with the triple stent.

OliveiraAlterations of blood flow pattern after triple stent endovascular treatment of saccular abdominal aortic aneurysm: a porcine model

Table 1. Distribution of aortic aneurysms blood flow measurements values.

Triple Stent Table Peak Systolic Velocity cm/s (PSV) Resistance index (RI)

Animal Pre-stent Post-stent Pre-stent Post-stent1 110.29 87.49 0.6/8 0.852 50.33 24.89 1.0 0.073 189.86 95.43 0.88 0.674 163.22 86.89 1.0 0.665 178.35 98.33 1.0 0.836 110.39 71.23 0.87 0.767 89.04 24.39 0.65 1.17

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R E S U M O

Objetivo: determinar as alterações do padrão do fluxo sanguíneo após tratamento endovascular do aneurisma sacular de aorta abdominal

com triplo stent. Métodos: estudo hemodinâmico de sete suínos das raças Landrace e Large White portadores de aneurismas saculares de

aorta abdominal infrarrenal artificialmente produzidos segundo técnica descrita. Os animais foram submetidos a implante de triplo stent

para correção endovascular do aneurisma e reavaliados por duplex scan quanto ao padrão do fluxo sanguíneo antes e após o implante

dos stents. A análise estatística foi realizada com o teste Mann-Whitney não pareado. Resultados: verificou-se uma queda significativa da

velocidade sistólica média de 127,4cm/s na fase pré-stent para 69,81cm/s na fase pós-stent. Houve ainda mudança no padrão do fluxo de

turbilhonar no saco aneurismático para laminar intrastent. Conclusão: o estudo demonstrou alterações do padrão do fluxo sanguíneo do

aneurisma sacular de aorta abdominal após tratamento endovascular com triplo stent.

Descritores: Fluxo Sanguíneo Regional. Aneurisma Sacular. Aneurisma da Aorta Abdominal. Stents. Suínos.

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Rev. Col. Bras. Cir. 2016; 43(3):

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Recebido em: 03/01/2016

Aceito para publicação em: 06/04/2016

Conflito de interesse: nenhum.

Fonte de financiamento: nenhuma.

Endereço para correspondência:

Jahir Richard de Oliveira

E-mail: jrichardoliveira@hotmail.com

OliveiraAlterations of blood flow pattern after triple stent endovascular treatment of saccular abdominal aortic aneurysm: a porcine model

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